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# Magoosh Brain Twister – Explanation: Now That’s Quite a Playlist

## Question

Highmont private school polled the graduating class of 125 for the musical genres they listen to. 88% indicated at least one of the following genres: indie rock, classical, country, and electronica. Of these students, 40% responded they listen to only one of the four genres. The average number of students within each distinct group of those who listen to exactly two genres is greater than the total number of those who listen to exactly three genres. If the only lack of overlap in musical tastes was in country and electronica, what is the greatest number of students who could listen to classical, country, and indie rock?

(A) 5
(B) 6
(C) 9
(D) 10
(E) 13

For this week’s question, Now That’s Quite a Playlist, I found the easiest way to organize all the information—and there is a lot of it—is to use a modified Venn diagram. We know that there is an overlap in all of the genres except country and electronica. Therefore, we can draw three circles, one each for classical, indie rock, and country, in the standard Venn diagram format. Next, we can draw a circle for electronica, overlapping it with classical and indie rock, but make sure that it doesn’t overlap with country. Now, we can start plugging in the relevant numbers.

First off, only 110 students answered the survey to begin with. 44 of those listened to one distinct genre. We don’t have to worry where those 44 go, since our focus is on the overlapping regions. What’s important is that leaves us with 66 for the overlapping regions. If we look at our diagram (and you should draw one out, if you haven’t already), there are five regions that encompass exactly two genres. The average of these has to be greater than the total. Play around with a few numbers. For instance, if we assume the average that encompasses exactly two genres is 10, then that would leave us with 16 (too many). Upping the average to 11 would give us 11 left over, which is almost what we want.

At this point, there is a little twist. We shouldn’t assume that since 11 didn’t work that we should plug in 12 (which would give us 6 left over). In other words, the average in each overlapping region of two genres doesn’t have to be an integer. Therefore, we could have 56 total in those regions that represent exactly two genres, leaving us with a total of 10 to divvy up. Remember, the only non-overlap is in country and electronica (surprise!), so each region of exactly three genres must have at least one. This leaves us with a maximum of ‘9’ that can represent classical, country, and electronica. Answer: (C).

### 7 Responses to Magoosh Brain Twister – Explanation: Now That’s Quite a Playlist

1. Vedant November 1, 2016 at 12:15 am #

I’m not sure i follow, your approach towards the end. Following the question, I formulated a Venn Diagram, with 4 genres consisting of 5 Intersections for students who listen to 2 genres and 2 Intersections for students who listen to 3 genres.

Therefore, Avg. of 5 Int + Intersection of Classical, Country & Indie + Intersection of Classical, Indie & Electronica = 66

For Max, assume Int of Classical, Country & Indie =1

Then, Avg. of 5 Int + Intersection of Classical, Indie & Electronica = 65

Now, Plugging in,
65-13=52
52/5=10.4
10.4<13
(E) is wrong.
65-10=55
55/5=11
Avg. of 11 is greater, this stands true.
Therefore Option (D) should be the right answer

• Magoosh Test Prep Expert November 1, 2016 at 9:17 am #

Hi Vedant,

This is almost correct, but there is one mistake that you’re overlooking.

Before we begin (this isn’t the primary mistake), but I think you meant “For Max, assume Int of Classical, Indie & Electronica = 1” when you stated, “For Max, assume Int of Classical, Country & Indie = 1” as we are solving for “Classical, Country & Indie.”

Next, for Answer (D), you got the average of the 5 intersections (exactly two genres) to be 11. And, we have that “Int of Classical, Country & Indie = 10”. BUT, don’t forget the “Int of Classical, Indie & Electronica = 1” we discussed before!

Remember, the question tells us that “The AVERAGE number (e.g., 11) of students within each distinct group of those who listen to exactly two genres is greater than the TOTAL number (e.g., 10 + 1 = 11) of those who listen to exactly three genres.

So, for Answer (D), you have 11 = 11. This can’t be, so you have to continue with your process that you were doing, and you’ll get to Answer (C) as correct!

2. Prerna August 21, 2014 at 12:35 pm #

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• Chris Lele August 22, 2014 at 11:46 am #

Prerna,

Wow, thanks so much for your awesomeness in sharing how you feel :). This just made my and my fellow Magoosher’s day 🙂

3. Sriram August 21, 2014 at 12:14 pm #

Chris,
I could be in the minority here, from the problem description, it was not clear to me the 110 count was to be the exact number of students surveyed,not inclusive of duplicates. I mean if x=sum of students liking 2 genre and y=sum of students liking 3 genre’s then, we end up with 110 = 44 + 2x + 3y and x>5y which leads to a different result. However, I like the ‘twist’ in the solution. Its ‘x’ and ‘y’ which needs to be integers and not the average. I think most of us would have missed it.

Thanks,
Sriram.

• Chris Lele August 22, 2014 at 11:43 am #

Hi Sriram,

Hmm…you’re the only one who has mentioned this so far. Even the content team at Magoosh didn’t see that as a possible interpretation. I’m not even quite sure what you mean by duplicates. If a student indicated listening to two genres, then the question is clear that they “only” or “exactly” liked that many genres. So I don’t think there is any ambiguity, but maybe I’m misinterpreting what you meant. The bottom line: we always want these questions as fair as possible :).

• Sriram August 22, 2014 at 12:02 pm #

Hi Chris,
Let’s assume we had just 2 genre’s, all else being the same for simplicity. So,
(a+x) + (b+x) = A+B, where ‘a’ and ‘b’ account for the exact number listening to only one genre and x is the no.of people who listen to both, that is, duplicate.
Therefore, for the problem above we’re assuming a+b+x=110 but it could be construed as A+B=110 leading to a+b+2x=110 …makes sense?
Thanks,
Sriram.

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